1. Field of the Invention
The present invention relates to a battery power supply device preferably used for an electric vehicle, such as a HEV (Hybrid Electric Vehicle), PEV (Pure Electric Vehicle) or FCEV (Fuel Cell Electric Vehicle), which uses an electric motor as at least a part of a power source.
2. Description of the Related Art
The electric vehicle, such as a HEV, PEV or FCEV, includes a high voltage battery power supply device for driving an electric motor of the electric vehicle. FIG. 3 illustrates a schematic structure of a conventional battery power supply device.
The conventional battery power supply device shown in FIG. 3 includes a battery pack 2 housed in a case 1. The battery pack 2 includes a plurality of battery modules 3 each provided in the form of a rod and a holder 4 in which the plurality of battery modules 3 are three-dimensionally disposed so as to be parallel to one another. Each battery module 3 includes a plurality of cells 5, which are serially connected together both electrically and mechanically, and is held by end plates 4a provided at both ends of the holder 4 with respect to the parallel battery modules 3. In the battery pack 2, the plurality of battery modules 3 are serially or parallelly connected together electrically. This allows a number of cells 5 to be serially connected together electrically so as to produce a prescribed high voltage.
In this conventional battery power supply device, in order to maintain the performance of the plurality of battery modules 3 parallelly arranged in the holder 4, an increase in temperature of each battery module 3 is required to be suppressed. Therefore, the battery pack 2 is structured such that the air flowing into the holder 4 as a cooling medium flows around each battery module 3 from one end to the other end of each battery module 3. Further, the battery pack 2 includes an inlet duct 6 and an outlet duct 7 respectively provided at both ends of the battery pack 2. A cooling fan 8 is provided in the inlet duct 6. The inlet and outlet ducts 6 and 7 project from the case 1.
Once the cooling fan 8 provided in the inlet duct 6 is activated, the air outside the case 1 is supplied to the battery pack 2 in the case 1 via the inlet duct 6 so as to flow around each battery module 3 in the battery pack 2 from one end to the other end of each battery module 3, thereby cooling each battery module 3. After cooling each battery module 3, the (heated) air is exhausted from the case 1 via the outlet duct 7.
In this conventional battery power supply device, each end plate 4a of the holder 4 included in the battery pack 2 is provided with a plurality of vent holes 4b so as to allow the flow of the air through the battery pack 2. The plurality of vent holes 4b provided in each end plate 4a have the same size and shape and are uniformly distributed over the end plate 4a. A cross-sectional area of the inlet duct 6 is sequentially increased along a direction from an upstream to a downstream direction of the air flow (hereinafter referred to as the “air flow direction”). On the other hand, a cross-sectional area of the outlet duct 7 is sequentially decreased along the air flow direction. The flow velocity of the air is reduced in the vicinity of a wall surface of the inlet and outlet ducts 6 and 7 due to the viscosity of the air.
Therefore, the air flowing into the inlet duct 6 is not distributed over the end plate 4a at a uniform flow velocity, and therefore the air flowing into the holder 4 via the vent holes 4b having the same size and shape is not distributed through the holder 4 at uniform flow velocity. As a result, flow velocity distribution of the air is not uniform in the holder 4, thereby causing the flow rate of the air to be nonuniform.
Specifically, at the center of the cross section of the holder 4 perpendicular to the air flow direction, flow velocity of the air is at its maximum and is sequentially decreased along directions from the center to the right, left, top and bottom. Accordingly, the flow rate of the air for cooling is sequentially decreased along a direction from the center of the cross section, which is perpendicular to the air flow direction, to the periphery, so that battery modules 3 disposed at the periphery sides are less efficiently cooled, whereby the battery modules 3 in the holder 4 are not uniformly cooled.
Further, layouts of the inlet and outlet ducts 6 and 7 are designed such that considerable pressure loss of the air is caused, and therefore the battery modules 3 in the holder 4 are not efficiently and uniformly cooled.
Furthermore, since the cooling fan 8 is provided inside the inlet duct 6, heat is generated by activating the cooling fan 8 with motor M, so that the air flowing into the holder 4 can be heated. As a result, the battery modules 3 in the holder 4 are not efficiently cooled.
Further still, the case 1 includes the battery pack 2 together with various electronic elements (not shown) provided so as to control the battery pack 2. When dew is formed through condensation due to temperature fluctuations and the presence of moisture in the case 1, these electronic elements can be easily rusted, short-circuited or deteriorated.
Any of these problems causes reduction in the performance of the conventional battery pack 2.